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Question
State the restrictions for having images produced by spherical mirrors to be appreciably clear.
Solution
- In order to obtain clear images, the formulae for image formation by mirrors or lens follow the given assumptions:
- Objects and images are situated close to the principal axis.
- Rays diverging from the objects are confined to a cone of a very small angle.
- If there is a parallel beam of rays, it is paraxial, i.e., parallel and close to the principal axis.
- In case of spherical mirrors (excluding small aperture spherical mirrors), rays farther from the principle axis do not remain parallel to the principle axis. Thus, the third assumption is not followed, and the focus gradually shifts towards the pole.
- The relation `("f" = "R"/2)` giving a single point focus is not followed, and the image does not converge at a single point, resulting in a distorted or defective image.
- This defect arises due to the spherical shape of the reflecting surface.
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